Regulation of tyrosine hydroxylase by gpe

ABSTRACT

Embodiments of this invention include methods for increasing the amount of the enzyme tyrosine hydroxylase (TH) in the central nervous system (CNS) of mammals in need of an increase in TH. Methods include the use of the tripeptide, gly-pro-glu (GPE) to increase TH in the CNS. GPE can increase the amount of TH and/or decrease the loss of TH in conditions characterized by a loss of dopamine, such as Parkinson&#39;s disease and CNS injury. GPE may act to increase the expression of TH or by inhibiting a decrease in TH expression within the CNS or by inhibiting the loss of TH-containing neurons within the CNS. By increasing the amounts of TH in the CNS, GPE can increase the amount of the neurotransmitter, dopamine, in areas of the CNS responsible for adverse symptoms of neural injury or disease.

[0001] This invention relates to methods of regulating the effect oftyrosine hydroxylase (TH). In particular it relates to increasing theeffective amount of TH in the central nervous systems (CNS) for thepurpose of increasing TH-mediated dopamine production in the treatmentof conditions such as Parkinson's disease.

BACKGROUND

[0002] Parkinson's disease is the second most prevalentneurodegenerative disorder after Alzheimer's. It is a chronic andprogressive motor system disorder and is distinguished by a tremor atrest, muscular rigidity, a slowness of movement initiation and movementexecution and a mask-like appearance to the face.

[0003] The cause of this disease is unknown but the symptoms are aconsequence of an 80% or greater loss of the dopaminergic neurons (whichproduce dopamine) in the pars compacta region of the substantia nigra(SNc).

[0004] Treatments available at present only target symptoms of thedisease. No drugs are currently available to intervene in the diseaseprocess. L-dopa is the most commonly employed current treatment (inorder to supplement dopamine levels within the CNS), but this haslimited and transient efficacy.

[0005] TH is a rate limiting enzyme for dopamine production.Upregulation of TH expression will therefore increase dopamineproduction in the CNS.

[0006] GPE is a tripeptide consisting of amino acids Gly-Pro-Glu. It andits dipeptide analogs Gly-Pro and Pro-Glu were first disclosed by Saraet al in EP 0366638. The suggestion made by Sara et al is that GPE hasneuromodulatory properties. GPE has also been established as havingneuroprotective properties and therefore having utility in theprevention or inhibition of neural cell death (WO 95/17204).

[0007] To date however, there has been no teaching or suggestion of GPEor its analogs having any direct effect on the effective amount of THpresent in the CNS or being able to intervene in the Parkinson's diseaseprocess.

OBJECT OF THE INVENTION

[0008] It is an object of this invention to provide new approaches totherapy or prophylaxis which involve directly upregulating theexpression of TH and TH-mediated dopamine production in CNS, or at leastto provide the public with a useful choice.

SUMMARY OF THE INVENTION

[0009] In a first aspect, the invention provides a method of treatmentof a patient suffering from or susceptible to a condition in which anincrease in the amount of TH present within the CNS is desirable, whichmethod comprises the step of increasing the effective amount of GPE oran analog thereof within the CNS of said patient.

[0010] In a further aspect, the invention provides a method of effectingan increase in the amount of TH within the CNS of a patient for therapyor prophylaxis of a neurological disorder or condition involvingdopaminergic neurons, said method comprising the step of increasing theeffective amount of GPE or an analog thereof within the CNS of saidpatient.

[0011] An “increase in the amount of TH” can be effected throughupregulation of expression of TH or a reduction in the loss ordegradation of TH.

[0012] By “analog” it is meant the dipeptides Gly-Pro and Pro-Glu aswell as any other small peptide which is capable of effectively bindingto the receptors in the CNS GPE binds to and of inducing an equivalentupregulatory effect upon the expression of TH.

[0013] In still a further aspect, the invention provides a method ofincreasing TH-mediated dopamine production within the CNS of a patient,said method comprising the step of increasing the effective amount ofGPE or an analog thereof within the CNS of said patient.

[0014] Most preferably, it is the effective amount of GPE itself whichis increased within the CNS of the patient. This can be effected bydirect administration of GPE and indeed this is preferred. However, theadministration of compounds which indirectly increase the effectiveamount of GPE (for example a pro-drug which, within the patient iscleaved to release GPE) is in no way excluded.

[0015] The active compound (GPE or its analog) can be administeredalone, or as is preferred, as part of a pharmaceutical composition.

[0016] The composition can be administered to the patient peripherally(for example by a parenteral route such as injection into the peripheralcirculation) or can be administered directly to the CNS. This latterroute of administration can involve, for example, lateralcerebro-ventricular injection, focal injection or a surgically insertedshunt into the lateral cerebro-ventricle of the brain of the patient.

[0017] Conveniently, the amount of TH is increased through theadministration of GPE or its analogs in the prophylaxis or therapy ofParkinson's disease.

[0018] It is also preferred that the increase of TH-mediated dopamineproduction is effected as part of therapy or prophylaxis of Parkinson'sdisease.

[0019] In a further aspect, the invention also consists in the use ofGPE or an analog thereof in the manufacture of a medicament for use inincreasing the amount of TH present in the CNS of a patient.

[0020] In still a further aspect, the invention consists in the use ofGPE or an analog thereof in the manufacture of a medicament for use inincreasing TH-mediated dopamine production for treating Parkinson'sdisease.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention is broadly as defined above. However, thosepersons skilled in the art will appreciate that it is not limited onlyto the above but that it also includes embodiments of which thefollowing description provides examples. A better understanding of thepresent invention will also be gained through reference to theaccompanying drawings in which:

[0022]FIG. 1 shows the number of TH immunopositive neurons followingtreatment with a control vehicle or with GPE two hours afteradministration of a neuro-toxin.

[0023]FIG. 2 shows the number of TH immunopositive neurons followingtreatment with a control vehicle or with GPE two hours afteradministration of a neuro-toxin.

[0024]FIG. 3 shows the density of TH immunopositive staining followingtreatment with a control vehicle or with GPE two hours afteradministration of a neuro-toxin.

[0025]FIG. 4 shows photomicrographs of immunohistochemical labeling ofthe SNc with an antibody against TH. A, C and E are at 10× magnificationand B, D and F are at 40× magnification. A and B are photomicrographs ofcontrol sections of the right side of the SNc. C and D arephotomicrographs from ipsilateral SNc where the vehicle was administeredintraventricularly 2 hours after lesioning with 6-OHDA. Note the majordecrease in TH immunoreactivity in C and the decreased immunoreactivityin the cell body and processes in D. E and F are photomicrographs of theipsilateral SNc where GPE was administered intraventricularly 2 hoursafter lesioning with 6-OHDA. Scale bars A, C, E 0.5 μm, B, D, F 20 μm.

[0026]FIG. 5 shows cell counts expressed as percent cell survival ofsubstantia nigra neurons after mechanical lesioning and treatment withGPE.

DESCRIPTION OF THE INVENTION

[0027] As indicated above, the present invention is broadly based uponthe applicants surprising finding that GPE and its analogs are capableof increasing the amount of TH within the CNS. This increase, which isthrough upregulating TH expression or through preventing the loss ordegradation of TH, is achieved through increasing the effectiveconcentration or amount of GPE or the analog in the CNS of a patient.

[0028] The effective increase in the amount of TH in turn effects anincrease in the production of dopamine within the CNS.

[0029] It is presently preferred by the applicants that GPE itself beused to increase the amount of TH/dopamine. Most conveniently, this iseffected through the direct administration of GPE to the patient.

[0030] However, while this is presently preferred, there is no intentionon the part of the applicants to exclude administration of other formsof GPE. By way of example, the effective amount of GPE in the CNS can beincreased by administration of a prodrug form of GPE which comprises GPEand a carrier, GPE and the carrier being joined by a linkage which issusceptible to cleavage or digestion within the patient. Any suitablelinkage can be employed which will be cleaved or digested to release GPEfollowing administration.

[0031] Another option is for GPE levels to be increased through animplant which is or includes a cell line which is capable of expressingGPE in an active form within the CNS of the patient.

[0032] GPE can be directly administered as part of a medicament orpharmaceutical preparation. This can involve combination of GPE with anypharmaceutically appropriate carrier, adjuvant or excipient. Theselection of the carrier, adjuvant or excipient will of course usuallybe dependent upon the route of administration to be employed.

[0033] The administration route can vary widely. An advantage of GPE isthat it can be administered peripherally. This means that it need not beadministered directly to the CNS of the patient in order to have effectin the CNS.

[0034] Any peripheral route of administration known in the art can beemployed. These can include parenteral routes with injection into theperipheral circulation being a suitable example. However, alternativeadministration routes selected from oral, rectal, nasal, subcutaneous,inhalation, intraperitonial or intramuscular can be employed.

[0035] Two of the most convenient administration routes will be bysubcutaneous injection (eg. dissolved in 0.9% sodium chloride) or orally(in a capsule).

[0036] It will also be appreciated that it may on occasion be desirableto directly administer GPE to the CNS of the patient. Again, this can beachieved by any appropriate direct administration route. Examplesinclude administration by lateral cerebro-ventricular injection orthrough a surgically inserted shunt into the lateral cerebro-ventricleof the brain of the patient.

[0037] The calculation of the effective amount of GPE or its analogs tobe administered will be routine to those persons skilled in this art.Needless to say, the final amount to be administered will be dependentupon the route of administration and upon the nature of the neurologicaldisorder or condition which is to be treated. A suitable dose range mayfor example be between about 0.04 mg to 1000 mg of GPE and/or analog per100 g of body weight where the dose is administered centrally.

[0038] For inclusion in a medicament, GPE and its analogs can beobtained from a suitable commercial source. Alternatively, GPE and itsanalogs can be directly synthesised by conventional methods such as thestepwise solid phase synthesis method of Merryfield et al. (J. Amer.Chem. Soc. 85 2149-2156 (1963)) Alternatively, synthesis can involve theuse of commercially available peptide synthesisers such as the AppliedBiosystems model 430A.

[0039] The present invention will now be illustrated with reference tothe following nonlimiting examples.

EXAMPLE 1

[0040] This experiment was blind with respect to the treatment (with GPEor the vehicle) and with respect to the counting of neurons expressingTH (between sections from animals treated with GPE or vehicle).

[0041] The objective of this experiment was to determine the effects ofadministering GPE on the expression of tyrosine hydroxylase (TH) in thepresence or absence of CNS injury. The experiment involved treating therats with a control vehicle or GPE 2 hours after a chemically inducedlesion in the substantia nigra region of the brain. Specifically, 9pairs of adult male Wistar rats (280-320 g) were prepared under 3%halothane/O₂ anaesthesia. The oxygen free radical producing neurotoxin6-hydroxydopamine (6-OHDA) which produces degeneration of dopamineneurones (8 μg/2 μl) was injected into the median forebrain bundle usinga 30 gauge needle (coordinates: anterior-posterior+4.7 mm, right+1.6 mm,vertical−8.5 mm). A guide cannula was placed on the dura 7.5 mm anteriorfrom stereotaxic zero and 1.5 mm from the midline on the right. The ratswere left to recover at room temperature. 2 hours after theadministration of 6-OHDA the rats were treated, via the guide cannula,with 3>g GPE or vehicle alone (15%1 injected with a pump rate of 2μl/minute, 0.1M acetate buffer [pH6], diluted 10 times in 0.1 bovineserum albumin in 0.1M phosphate buffered saline [PBS][pH7.31]).

[0042] The rats were sacrificed using pentobarbital 14 days after 6-OHDAinduced injury. Brains were perfused with normal saline and 4%paraformaldehyde and fixed in perfusion fixative overnight. The brainswere paraffin embedded using a standard processing schedule. Sections (8μm) were cut through the substantia nigra using a microtome.Immunoreactivity for TH was established with sections mounted on chromealum coated slides. Briefly, the sections were dewaxed, rehydrated andwashed in 0.1M PBS. The sections were pre-treated with 1% H₂O₂ in 50%methanol for 20 minutes and then washed in 0.1M PBS (5 minutes×3). Theantibodies were diluted in 1% goat serum. The sections were thenincubated with rabbit (Rb) anti-TH (1:500) antibodies (the primaryantibodies) for 2 days. The sections were washed using 0.1M PBS (5minutes×3) and then incubated with goat anti-rabbit biotinylatedsecondary antibodies (1:200) at room temperature overnight. The sectionswere washed in 0.1M PBS (5 minutes×3) and then incubated in (ExtrAvidin™Sigma 1:200) for 3 hours and followed by H₂O₂ (0.01%) in3,3-diaminobenzidine tetrahydrochloride (DAB, 0.05%) reaction. Thesections were then dehydrated and coverslipped.

[0043] The neurons in the pars compacta region of the SNc at 3 levels inboth hemispheres which showed specific immunoreactivities correspondingto TH were counted using a light microscope. The total counts of neuronswere compared between the GPE and the vehicle treated group. Data wereanalysed with paired t-test and presented as mean±sem. The results arepresented in FIG. 1.

[0044]FIG. 1 shows that the number of TH immunopositive dopaminergicneurons increased with GPE on the lesioned (right) side of the brain.This indicates that the administration of GPE is effective inupregulating TH expression.

EXAMPLE 2

[0045] Example 2 was performed using a second set of rats (9 pairs),using the same experimental parameters except that only theimmunopositive neurons at 2 levels of the SNc were counted.

[0046] The results are shown in FIG. 2, and again demonstratedupregulation of TH expression.

EXAMPLE 3

[0047] Ethics Approval

[0048] These experiments were approved by the University of AucklandAnimal Ethics Committee and all efforts were made to minimise thesuffering incurred and the numbers of animals used.

[0049] Experimental Design and Animal Preparation

[0050] A paired experimental design was used and the experimenter wasblinded to the treatment groups. Eighteen male Wistar rats (50-60 daysold, 280-310 g) were used for this study. 6-hydroxy dopamine (6-OHDA)was prepared as ⁸ μg in a base of 2 μl 0.9% saline containing 1%ascorbic acid. It was administered into the right medial forebrainbundle (MFB) using coordinates of AP+4.7 mm, R 1.6 mm, V−8 mm underanaesthesia of 3% halothane. 6-OHDA was injected into the right MFBusing a Hamilton syringe (100 μl with a 30G needle) controlled by amicrodialysis infusion pump at an infusion rate of 0.2 μl/minute. Theinfusion needle was then slowly withdrawn 5 minutes after the infusion.The surgery and procedures for the intracerebroventricularadministration have been described by Guan et al (1993), Journal ofCerebral Blood Flow and Metab, 13, 609-616. Briefly, a guide cannula(21G, 6 mm) was fixed on the top of the dura with coordinates of AP+7.5mm, R 1.5 mm immediately after the injection of 6-OHDA. Either GPE (3μg/15 μl) or its vehicle were infused into the right lateral ventricle 2hours later at an infusion rate of 2 μl/minute. Rats were then housed ina holding room with food and water ad libitum for the next 2 weeks.

[0051] The rats were then deeply anaesthetized with an overdose ofpentobarbital and transcardially perfused with normal saline followed by10% buffered formalin. The brains were removed from the skull and keptin the same fixative for the next 48 hours. A standard paraffin tissuepreparation was used to process the tissue so that it could be used forimmunohistochemistry. Coronal sections (8 μm) were cut using amicrotome, and the sections were mounted on chrome alum coatedmicroscopy slides and air-dried. SNc sections used forimmunohistochemical staining were deparaffinized, rehydrated and washedin PBS (0.1M). The sections were then pretreated with 1% H₂O₂ for 20minutes, washed with 0.1M PBS (3×5 minutes) and incubated with rabbitpolyclonal antisera raised against tyrosine hydroxylase (Protos Biotech,USA) diluted 1:500 with 1% goat serum for 48 hours at 40° C. Thesections were washed in PBS (3×5 minutes) and incubated with donkeyanti-rabbit biotinylated secondary antibody (1:200, Amersham, LifeScience) overnight at room temperature. The sections were washed,incubated in streptavidin-biotinylated horseradish peroxidase (1:200,Amersham, Life Science) for 3 hours, washed again in PBS and thenreacted in 0.05% 3,3-diaminobenzidine tetrahydrochloride (DAB) and 0.01%H₂O₂ to produce a brown reaction product. The sections were dehydratedin a graded alcohol series, cleared in xylene and coverslipped withmounting medium.

[0052] Tissue Evaluation and Statistics

[0053] The number of TH positive neurons on both sides of the SNc werecounted using light microscopic examination (20× magnification) at threerepresentative levels (AP+4.2, +3.8 mm and 3.4 mm) (Paxinos, et al(1982), New York: Academic Press). The average density from thebackground was also measured. The analyst was blinded to the treatmentand control groups. The difference in average density between thebackground and TH immunostaining was calculated and used for dataanalysis. Right/left (R/L) ratios of both the number of THimmunopositive neurons and the average density of TH immunostaining fromeach level was compared between the two treatment groups using one wayANOVA. Data are presented as mean±SEM.

[0054] Results

[0055]FIG. 3 shows that TH immunoreactivity was restored with GPE on thelesioned (right) side of the brain. This effect was more pronounced incaudal levels (16±11.2 to 99.6±27%) compared with the rostral level(FIG. 3). This indicates that the administration of GPE is effective andselective in upregulating TH expression.

[0056] GPE treatment restored the density of TH immunostaining in boththe cytoplasm and processes of neurons (FIG. 4).

[0057] GPE also showed 99.6±27.0% restoration in TH immunoreactivitywith only 60±13.0% neuronal survival in the most caudal level analysedof the SNc.

DISCUSSION/CONCLUSIONS

[0058] The above example shows the effect of GPE administration on THexpression in the SNc. GPE was particularly effective in upregulating THexpression in the most caudal region of SNc analysed. GPE upregulated THexpression in the cytoplasm of both the neuronal cell body and neuronalprocesses. GPE prevented the loss of TH immunopositive neurons in theSNc compared to the control group. GPE provided protection for thedopaminergic neurons against the neurotoxin 6-OHDA.

EXAMPLE 4

[0059] Ethics Approval

[0060] These experiments were approved by the University of AucklandAnimal Ethics Committee and all efforts were made to minimise thesuffering incurred and the numbers of animals used.

[0061] Medial Forebrain Bundle Transection and Cannulation

[0062] Adult male Wistar rats (200-220 g) were anaesthetized with 75mg/kg Nembutal and positioned in a stereotaxic apparatus. Unilateraltransection of the medial forebrain bundle which contains the ascendingnigral dopaminergic projection fibers was made 1.3 mm rostral to therostral tip of the SNc using a retractable wire knife (David KopfInstruments, Tujunga, Calif.). The knife was lowered into the brainusing the following coordinates from the atlas of Paxinos and Watson(1986), Sydney: Academic Press: 3.3 mm posterior to Bregma, 2.4 mmlateral from midline, and 8.5 mm ventral from skull, the blade wasextended 2.0 mm toward midline, raised 2.5 mm dorsally, retracted andextended again, and then returned 2.5 mm ventrally. The wire blade wasretracted and the knife withdrawn. Next, a 22-gauge metal guide cannulawas permanently fixed into place supranigrally at 5.0 mm posterior toBregma, 2.0 mm lateral to midline, and 6.8 mm ventral to skull. A secondset of intact unlesioned rats were cannulated supranigrally at the samecoordinates.

[0063] Neurotrophic Factor Infusion

[0064] Animals received daily supranigral injections of trophic factorsvia a Hamilton syringe attached to a 28-gauge cannula 1 μl of either GPE(0.3 μg/μl), or 1 μg of the control vehicle PBS with 0.1% bovine serumalbumin (BSA) beginning immediately after lesioning and extending fortwo weeks post-lesioning. GPE was diluted in phosphate buffered saline(PBS) containing 0.1% BSA (pH 7.4).

[0065] Immunocytochemistry

[0066] After two weeks of treatment, animals were perfused under deepanaesthesia with PBS (pH 7.4) followed by 4% paraformaldehyde inphosphate buffer (pH 7.4). Brains were post-fixed for 24 hours at 4° C.in the same fixative then transferred sequentially to 10% and 30%sucrose in PB for 2-5 days until sunken. Floating 30 μm coronal nigralsections were stained by avidin-biotin-peroxidase immunocytochemistry.Rabbit anti-rat tyrosine hydroxylase (TH) polyclonal antibody (TE101,Eugene Tech International, New Jersey, USA) was diluted 1:100 in PBScontaining 0.2% Triton X-100, 3% goat serum, and 0.02% sodium azide.Sections were first incubated for 1 hour at room temperature in primaryantibody vehicle. Incubation with the primary antibody was for 3-4 daysat 40° C. Biotinylated anti-rabbit IgG (Vector Laboratories) secondaryantibody was diluted at 4 μl/ml in PBS containing 0.1% Triton X-100 andnormal rabbit serum. Sections were incubated for 2 hours at roomtemperature, followed by an avidin-biotin-peroxidase cocktail (VectorLaboratories) incubation for 1 hour at room temperature. Peroxidase wasvisualized with 1 mg/ml 3,3′-diaminobenzidine in 0.03% H₂O₂ for 5minutes. Controls were conducted by replacing the primary antibody withpre-immune IgG or by omitting the primary and/or secondary antibody fromthe procedure. Sections were mounted on gelatin-coated slides,dehydrated in serial ethanol, cleared in xylene and coverslipped withmounting media.

[0067] Quantificaton of Cell Number

[0068] Immunopositive cells were counted in the central SNc Counts weremade ventral and lateral to the lemniscus medialis, including both thepars compacta and pars reticulata, but excluding the ventral tegmentalarea in the ventromedial midbrain and the retrorubral field in thecaudolateral midbrain. A cell was counted if it had an intact cell bodyand soma membrane. Counts were taken on both the contralateral andipsilateral sides from 2-3 animals per treatment. The number of cellswas represented by the mean number of immunopositive cells within thedescribed field on each side of the brain. To reveal percent survival,percent changes were calculated by dividing the ipsilateral value bycontralateral value.

[0069] Results

[0070] The percent cell survival of TH immunopositive neurons increasedwith GPE treatment on the lesioned side of the brain (FIG. 5). Thisindicates GPE is effective in upregulating TH expression.

[0071] Discussion

[0072] The above examples show the effect of GPE administration on THexpression in the pars compacta region of the SNc.

INDUSTRIAL APPLICATION

[0073] The experimental results demonstrate the ability of GPE toincrease the amount of TH in the CNS through a direct increase in enzymeexpression. In turn, the increased expression of TH leads to an increasein TH-mediated dopamine production.

[0074] These findings make GPE and its analogs applicable in treating anumber of neurological disorders or conditions, either therapeuticallyor prophylactically. Indeed, it will be apparent to those personsskilled in the art that GPE and its analogs can be employed at any timewhere a patient would benefit from an increase in the expression ofTH/dopamine within the CNS. Neurological disorders or conditions whichwould benefit from this include, but are not limited to Parkinson'sdisease.

[0075] It will be appreciated that although the present invention isdescribed above with reference to certain specific embodiments, thedescription provided is exemplary only and that the invention is notlimited thereto.

1. A method of treatment of a patient suffering from or susceptible to acondition in which an increase in the amount of tyrosine hydroxylase(TH) with the central nervous system (CNS) of said patient is desirable,which method comprises the step of increasing the effective amount ofGPE or an analog thereof within the CNS of said patient.
 2. A method ofeffecting an increase in the amount of tyrosine hydroxylase (TH) withinthe CNS of a patient for therapy or prophylaxis of a neurologicaldisorder or condition involving dopaminergic neurons, said methodcomprising the step of increasing the effective amount of GPE or ananalog thereof within the CNS of said patient.
 3. A method of treatmentof a patient suffering from or susceptible to a condition in which anincrease of tyrosine hydroxylase (TH)-mediated dopamine production isdesirable, which method comprises the step of increasing the effectiveamount of GPE or an analog thereof within the CNS of said patient.
 4. Amethod of treatment as claimed in claim 1, claim 2 or claim 3 whereinthe concentration of GPE or an analog thereof is increased byadministering to said patient an effective amount of GPE or said analogof GPE or of a prodrug thereof.
 5. A method of treatment as claimed inclaim 1, claim 2 or claim 3 wherein the concentration of GPE isincreased in the CNS by direct administration of GPE.
 6. A method asclaimed in any one of claims 1 to 5 which is prophylactic.
 7. A methodas claimed in any one of claims 1 to 5 which is therapeutic.
 8. A methodof treatment or prophylaxis of Parkinson's disease in a patient, whichmethod comprises increasing tyrosine hydroxylase (TH)-mediated dopamineproduction by dopaminergic neurons within the substantia nigra of theCNS by the step of increasing the effective amount of GPE or an analogthereof within the CNS of said patient.
 9. The use of GPE or an analogthereof in the preparation of a medicament for use in increasing theamount of tyrosine hydroxylase (TH) within the CNS of a patient fortherapeutic or prophylactic purposes.
 10. The use of GPE or an analogthereof in the preparation of a medicament for use in the treatment ofParkinson's disease mediated by increasing expression of tyrosinehydroxylase (TH).
 11. The use of GPE or an analog thereof in thepreparation of a medicament for use in increasing tyrosine hydroxylase(TH)-mediated dopamine production within the CNS of a patient.
 12. Theuse of GPE or an analog thereof in the preparation of a medicament foruse in increasing tyrosine hydroxylase (TH)-mediated dopamine productionby dopaminergic neurons in the substantia nigra of the CNS in order totreat Parkinson's disease.